Caveman bone part sheds light on our past

Neanderthal study among first to map extinct species' DNA

A 38,000-year-old bone fragment is opening doors to greater understanding of human origins by unraveling mysteries about one of our most enigmatic distant relatives: the Neanderthal.

An international team of researchers is sequencing the Neanderthal genome using the half-ounce fragment from a male found in a Croatian cave. Already, it is giving up some secrets: Neanderthals and humans split from a common ancestor 500,000 years ago, and they didn't interbreed, at least on a large scale.

The findings reported yesterday are preliminary. As the research continues, scientists hope to determine much more about when humans developed genetic traits that made them unique, such as brain size and the ability to speak a language. It might also help unravel the mystery of why Neanderthals disappeared.

"We're going to be able to learn about the biology, learn about the things we never could have learned just from the stones and the artifacts," said Edward M. Rubin, director of genomics at the Lawrence Berkeley National Laboratory and a senior author of one of two papers describing the study.

The journals Science and Nature jointly reported the results of work being done by the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, which teamed up with a Connecticut-based company, 454 Life Sciences, and a group from the Berkeley lab. The sequencing is expected to take two more years to complete.

The study is one of the first major efforts at sequencing the DNA of an extinct species.

Neanderthals lived in Europe and western Asia for more than 200,000 years before they vanished 30,000 years ago. Modern humans evolved about 100,000 years ago in Africa before they wandered into Europe and Asia, where Neanderthals also lived.

The researchers concluded that the Neanderthal genome is 99.5 percent identical to that of humans today. By contrast, the chimpanzee genome is about 98 percent identical. Chimpanzees and humans split from a common ancestor 6 million years ago.

The research is unlikely to lead to any immediate drug therapies, diagnostic tools or other practical benefits, the authors say. But it should help scientists identify recent developments in our evolutionary history by comparing the genetic makeup of Neanderthals with the genetic maps of humans and chimpanzees. The human genome was sequenced in 2001, and the chimpanzee genome was sequenced last year.

"The question that it addresses is, when did the handful of changes occur that made us us, and that's a fascinating question," said Hendrik Poinar, an expert on ancient DNA at McMaster University who wasn't part of the studies.

Other scientific groups had obtained DNA from extinct cave bears and ancient mammoths.

The research teams say their findings confirm that it's possible to completely sequence the genomes of certain types of extinct life forms. But it isn't easy. Time degrades the organic molecules that make up DNA, so sequencing a genome is impossible if the remains are too ancient, the researchers say. Don't expect to see a DNA analysis of Lucy, the famous 3 million-year-old hominid fossil found in Ethiopia.

"I don't think you can do it for anything more than 100,000 years old," said Richard E. Green, a postdoctoral fellow and researcher at the Max Planck Institute.

The bone used in the study was found in Croatia in the back of a cool cave, in a dry spot. Well preserved and not contaminated by excessive handling by people, the fragment was found to be a good sample for sequencing.

Some skeptics argue that we might not learn much about ourselves from Neanderthal genetics, because many of the important steps in our evolutionary development occurred millions of years before Neanderthals appeared.

"Think of a parfait. This is the kind of thing that can be good for telling you what's in the upper level. ... But it doesn't tell you what's lower down in the cup. From an evolutionary standpoint, that's where a lot of the important information is," said Owen C. Lovejoy, a human anatomist at Kent State University.

What defines a Neanderthal - the thickly muscled body, sloping forehead and extended jaw popularly seen in depictions of cavemen - is largely based on fossil remains scattered throughout Europe and Asia. The name comes from the Neander Valley in Germany where the first remains were discovered in 1856.

However, DNA analysis could rewrite some of that history. Scientists liken DNA to a computer program, written in the form of long chains of chemicals called "bases" that are referred to by their initials: A, T, C and G. Different strings of these letters form different genes.

Humans, Neanderthals and chimps all have 3 billion base pairs and have experienced millions of "evolutionary events" that have changed the order of letters in some way. By tracking those changes and mutations in the genetic code, researchers can look back in time to decipher when two species split from a common ancestor or when they developed specific genetic traits.